This invention relates to a seal mechanism for a Stirling engine of the type having a displacer piston and a power piston slidably disposed inside a single cylinder.
In conventional Stirling engines, it is common to form a seal between the displacer piston and the cylinder wall by two sets of three-piece piston rings mounted on the displacer piston with a space therebetween. Each of the three-piece piston rings comprises two loosely-fitting outer rings which are stacked on top of one another and an inner ring disposed inside the outer rings. The power piston also has one or more similar three-piece piston rings mounted thereon. With this type of seal mechanism, there is the problem that fluttering of the displacer piston rings can easily develop due to the back and forth movement of the displacer piston. Due to the fluttering, a complete seal can not be obtained between the compression space and the expansion space of the engine, resulting in decreased engine output and thermal efficiency.
There is also the problem that it is easy for foreign matter such as dirt to enter the ring grooves of the displacer piston and the power piston, reducing the sealing ability of the piston rings and causing variation from cycle to cycle in the pressure in the compression space and the buffer space of the engine, as a result of which the output of the engine is unstable.